1. Field of the Invention
This invention relates to a valve system for an automobile engine, and more particularly to a mechanism for driving a rocker arm of a valve system for an OHC type engine.
2. Description of the Related Art
As is wellknown, with a valve system for an OHC (overhead camshaft) type engine, one end of a seesaw rocker arm is in contact with a driving cam and the other end is in contact with valve stem ends to open and close valves in response to the movement of the cam.
With such a valve system, there have been proposed mechanisms for selectively stopping operation of valves and cylinders to save fuel during low speed and low load running, and for operating the valves efficiently to enhance air intake and gas exhaust during high speed running.
FIG. 26 of the accompanying drawings is a cross-sectional view showing a structure of one example of the foregoing mechanism for stopping reciprocation of valves. In FIG. 26, a reciprocative plunger C is located at a non-rocking portion of a rocker arm A. The plunger C confronts a stop plate D which is movable perpendicularly to the moving direction of the plunger C and has a circular opening D1 at the center thereof as shown in FIG. 27. The plunger C is passable through the opening D1. In FIG. 26, I stands for a rocker shaft.
One end of the stop plate D is coupled to a piston E, which is slidable perpendicularly in the moving direction of the plunger C above the rocking center of the rocker arm A. The piston E is driven by pressure in an oil gallery F connected to a non-illustrated oil pressure controller.
Normally, bias of compression springs G and H causes the plunger C to project toward the valve stem end B, and the piston E to prevent the center of the circular opening D1 of the stop plate P from being in agreement with an axis of the plunger C. (Refer to Column on "3. Valve Stopping Unit", page 161 of "Structure of Gasoline Engine", published by Sankaido Co., Ltd., for example.)
With the foregoing structure, during low speed and low load running, pressured oil from the oil pressure controller causes the piston E to slide to the right against the bias of the compression spring H as shown in FIG. 28. In response to the piston E, the stop plate D is moved to the right, thereby letting the circular opening D1 of the stop plate D agree with the axis of the plunger C. When the rocker arm A is rocked by the valve driving cam (by an angle .theta. shown in FIG. 28), rocking motion of the rocker arm A is not transmitted to the plunger C. Therefore, the valve stem end B is not reciprocated, thereby preventing the valves from being opened and closed.
With the foregoing structure, the valve driving mechanism as well as the plunger C for reciprocating the valve stem is disposed at the rocking portion which is far from the base of the rocker arm. Heavy weight is applied to the rocking portion of the rocker arm, which increases inertia mass, and makes the rocker arm rather slow to operate the valves efficiently during high speed running.
Since various components are mounted at the rocking portion of the rocker arm, the rocking portion becomes inevitably complicated. When this structure is applied to a valve system for a DOHC (double overhead camshaft) type engine in which valves are disposed side by side, it is impossible to achieve the primary object to reduce fuel cost and improve air intake and gas exhaust efficiency because of lack of a space for the above-described mechanism.